My car had misfire/running on 5 cyclinders during idle, and also hesitation/stuttering/whatever you call it at mid rpm or when it was trying to come on boost earlier this year.
The misfire was due to blockage in injectors (I run E85 and occasionally BP/Shell 98). Mechanic cleaned all the injectors and problem solved.
However still having the hestitation during mid rpm. Mech did all the mechanical checks and couldn't find anything so deemed it has to be electronic problems. So I replaced my old splitfire with brand new ones and bought brand new OEM loom. Problem solved.
From my researches, spark plugs, injectors, fuel systems, coilpacks are the common issues. So you are on the right track, just need to track it down I guess.
Although the platinum plugs SHOULD last 100k kms but they still have a chance to get faulty before that. As per @zebra, getting some cheap copper plugs to check wouldn't hurt.
Hopefully this helps.